iwlwifi: mvm: write queue_sync_state only for sync

We use mvm->queue_sync_state to wait for synchronous queue sync
messages, but if an async one happens inbetween we shouldn't
clear mvm->queue_sync_state after sending the async one, that
can run concurrently (at least from the CPU POV) with another
synchronous queue sync.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 3c514bf8

 ("iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201107104557.51a3148f2c14.I0772171dbaec87433a11513e9586d98b5d920b5f@changeid